docs(readme): Add README detail

Author: Walker

README.md

@@ -1,2 +1,164 @@
 # asset-pipe-css-reader
 
+A module that takes any number of css feed streams (provided by asset-pipe sinks) and bundles them into a readable stream of css content.
+
+This is an internal module intended for use by other modules in the [asset-pipe project](https://github.com/asset-pipe).
+
+## Overview
+
+Given any number of css feed streams, the reader will:
+1. Merge streams into a single stream
+2. Dedupe any items with identical id hashes keeping the last occurrence
+3. Ensure order of streams given is preserved for the final output CSS
+
+### Input data format
+
+The following is an example of a feed file:
+(Something like /path/to/feeds/feed-a.json)
+
+```js
+[
+    {
+        // Unique id for entry. Created by hashing together name, version and file
+        id: '4f32a8e1c6cf6e5885241f3ea5fee583560b2dfde38b21ec3f9781c91d58f42e',
+        name: 'my-module-1',
+        version: '1.0.1',
+        file: 'my-module-1/main.css',
+        // bundled css content with any @import statements inlined
+        content: '/* ... */'
+    }
+]
+```
+
+## Installation
+
+```bash
+npm install asset-pipe-css-reader
+```
+
+## Usage
+
+### Require the reader
+```js
+const CssReader = require('asset-pipe-css-reader')
+```
+
+### Instantiating the reader
+
+Either pass a single stream created by an asset-pipe sink:
+```js
+const sink = new SinkFs({
+    path: '/path/to/css/feeds'
+});
+const feedStream = sink.reader('feed-a.json');
+const reader = new CssReader(feedStream)
+```
+
+Or pass an array of streams:
+```js
+const sink = new SinkFs({
+    path: '/path/to/css/feeds'
+});
+const feedStream1 = sink.reader('feed-a.json');
+const feedStream2 = sink.reader('feed-b.json');
+const reader = new CssReader([feedStream1, feedStream2])
+```
+
+### Consuming content from the reader
+
+You should wait for the reader to become ready by listening for the `pipeline ready` event.
+
+The reader is a readable stream so in order to access the data you may register a data handler
+and listen for chunks to be passed to the handler:
+```js
+reader.on('pipeline ready', () => {
+    reader.on('data', data => {
+        // ..
+    })
+})
+```
+
+You might also pipe the reader into a writeable or transform stream:
+```js
+const { writeFile } = require('fs')
+const consumer = writeFile('/path/to/save/file')
+
+reader.on('pipeline ready', () => {
+    reader.pipe(consumer)
+})
+```
+
+## API
+
+### Methods
+
+#### constructor
+
+Constructor takes a single stream or array of streams. Streams should be produced with an asset-pipe sink such as: 
+- [asset-pipe-sink-s3](https://github.com/asset-pipe/asset-pipe-sink-s3`)
+- [asset-pipe-sink-fs](https://github.com/asset-pipe/asset-pipe-sink-fs`)
+- [asset-pipe-sink-gcs](https://github.com/asset-pipe/asset-pipe-sink-gcs`)
+- [asset-pipe-sink-mem](https://github.com/asset-pipe/asset-pipe-sink-mem`)
+
+Examples
+```js
+new CssReader(stream)
+```
+```js
+new CssReader([stream, ...stream])
+```
+
+Returns: `Readable Stream`
+
+### Events
+
+#### file found
+
+Event produced whenever an underlying feed stream successfully reads its feed
+file from disk
+
+```js
+cssReader.on('file found', file => {})
+```
+
+Param: `file`, name of the file given to the feed stream to read from
+
+#### file not found
+
+Event produced whenever an underlying feed stream is unable to read its feed
+file from disk
+
+```js
+cssReader.on('file not found', file => {})
+```
+
+Param: `file`, name of the file given to the feed stream to read from
+
+#### pipeline ready
+
+Event produced once all feed file streams have been successfully merged into
+a pipeline
+
+```js
+cssReader.on('pipeline ready', () => {})
+```
+
+#### data
+
+Event that emits chunks of CSS content to a consumer
+
+```js
+cssReader.on('data', chunk => {})
+```
+
+Param: `chunk`, a piece of CSS text
+
+#### error
+
+Event produced whenever any of the various stages of the pipeline emit errors
+
+```js
+cssReader.on('error', err => {})
+```
+
+Param: `err`, Error forwarded from merged streams or otherwise emitted from the pipeline